1. Field of the Invention
The present invention relates to an apparatus and a method for measuring and identifying the electric field strength generated from each of transmitters arranged in a detection target space by a receiver to grasp a state of an object such as a person or a thing.
2. Description of the Related Art
RFID (the abbreviation of Radio Frequency IDentification) refers to what is for exchanging information with a tag in which ID information is embedded, via short-distance wireless communication using an electromagnetic field, a radio wave or the like, and also refers to the whole technology therefor.
Especially in Japan, the movement of attempting to apply the RFID technology to the fields of welfare and crime prevention has gathered momentum with the advent of the aged society. For example, it is under examination to realize, in a hospital, information support so that a medical staff can efficiently work by attaching RFID tags to the medical staff, patients, medical equipment and medical products, collecting location information about persons and things by antennas arranged at various places via a network such as a LAN, and performing centralized control of the location information by a server, and to utilize the RFID tags for location management of prisoners in a prison.
It is also conceivable to realize higher quality services by mounting various sensors on RFID tags, attaching the RFID tags to persons, detecting a particular state and an abnormal state of the person or things, transmitting information about the state and processing collected information.
However, in the fields of welfare and crime prevention, places to be monitored are often private spaces of people who are to receive services, and they hate to attach a device in such spaces. They may forget to attach the device. Even if devices are attached to prisoners in a prison, a prisoner who does not want to be known of his state may pretend to attach the device. Detailed examples will be described below.
Statistically, a bathroom, a restroom and a dressing/undressing space account for a high percentage among places where elderly people fall down because of a brain or heart attack. There exists medical technology in which earlier discovery enables more appropriate treatment to significantly reduce aftereffects. It is necessary, in such particular closed spaces where only an elderly person exists and early discovery by a third person is difficult, to detect a state in which the elderly person has fallen down and cannot move and inform it to a person in charge of nursing care as soon as possible.
As described in Japanese Patent Laid-Open No. 11-151209, in a nursing care home, a nurse goes around checking patient rooms and beds because it is necessary to grasp whether patients are in beds provided in the patient rooms, that is, whether the patients are sleeping in the beds or wandering away from the beds in order to grasp the patients' absence-from-bed/presence-in-bed states. However, it is impossible to continuously go around checking all the patients' beds. Thus, it is necessary to detect a state in which an elderly person does not exist in a particular space, i.e., on a bed, and inform it to a person in charge of nursing care of the elderly person as soon as possible.
From the viewpoint of crime prevention, bad deeds taking advantage of cognitive impairment of elderly persons are increasing, such as violence and robbery of money and valuables in nursing care homes. In order to cope with this, it is necessary to record an abnormal movement around a bed and take a picture of persons who exist at that time. However, since an elderly person or his or her guardian hates a camera being placed in the room, it is necessary to install the camera outside the room. That is, it is necessary to take a picture of a person who comes out of the room immediately after it is detected that the movement of the elderly person is abnormal in the particular space, i.e., around the bed, to record and identify the suspicious person.
In business companies, acts of information collectors infiltrating inside offices, such as industrial spies, are a problem. An event was reported and much talked about that data was stolen from a computer to leak technical information to a foreign company. Such a primitive method has been repeated again and again to steal information. In order to prevent this, it is proposed to have employees carry RFID tags, install an antenna in an individual employee's booth and take a picture when an employee having a different ID intrudes into a booth. However, an employee with a malicious intention does not do such a malicious act with his own ID attached to him. That is, it is necessary to detect and record existence of a third person other than the person in charge of the booth, even if the third person does not have any ID.
As described above, in the fields of welfare and crime prevention, it is much more often appropriate to install a sensor-attached RFID tag in a space where a problem may occur to collect information rather than attaching a sensor or an RFID tag to a detection target. Since it is often the case that positions where a problem may occur are distributed in multiple places, it is desirable to reduce the cost by adapting the sensor be able to monitor a wide range of space, or assigning one sensor to each of the multiple places and minimizing the function of the sensor itself.
A network camera is a sensor having a function of detecting a state of a person or a thing and transmitting information not by being attached to a human body but by being provided in an environment. The network camera makes it possible to obtain information from which a state of a person lying down, a state of receiving violence, or the like can be judged. However, a great amount of information is used to detect a simple state, and there is a disadvantage that the information transmission cost and the information processing cost are high. Furthermore, consideration must be given to a privacy problem to install a camera in a private space.
A current-collection-type infrared sensor can contactlessly collect states of a person or a thing similarly to a camera while securing privacy, and the amount of information is not large, and the information processing cost is low. However, it is known to be easily affected by steam, dust or stain and excessively issue a wrong signal.
A Doppler radar used for an activation switch of an automatic door and the like does not malfunction due to steam, dust or stain, and its function is sufficient to detect existence. However, its installation is large-scale. In Japanese Patent Laid-Open No. 2004-226089, a lock control apparatus is proposed as a Doppler-radar-type sensor for which the large-scale installation and cost problems have been overcome. However, since the Doppler-radar-type sensor is a radar capable of observing not only the position but also the moving speed of an observation target by observing variation in frequency due to the Doppler effect, it has functions unnecessary for detecting a still state as described above, and the cost per sensor is higher for the functions.